It's been one year since 19-year-old Tanner Krupa was found murdered in Surrey, B.C., and his family is still waiting to see his killers identified and brought to justice.

On Tuesday, police marked the grim anniversary of Krupa's death by releasing a heartbreaking video statement from his mother, who pleaded for tips that could help solve her son's murder.

"We have no answers yet, and we are grieving without any closure at all," she said.

Krupa's body was discovered in a laneway near Kwantlen University in the early morning hours of Aug. 20, 2017.

He had been working as a direction driller and intended to start university in the fall, according to his mother, who described Krupa as a big-hearted young man who never got into trouble.

"Tanner did not have a criminal record," she said. "Never in a million years would we have thought that Tanner would pass away under such horrible circumstances."

Officers found him dead while responding to reports of an altercation in a quiet residential neighbourhood.

At a news conference Tuesday, the Integrated Homicide Investigation Team said police now believe a group of men were involved in the altercation that killed Krupa, but that some of them only watched from the sidelines.

"Investigators believe that some of the males did not participate, but were bystanders with first-hand information about what happened to Tanner," Cpl. Frank Jang said.

Jang called on any of those men to come forward and help give closure to the victim's grieving loved ones.

"Unburden your conscience," he said. "Help us make things right. It's never too late to do the right thing."

Investigators believe the men were driving around in two vehicles, a white Toyota Corolla and a white Honda Civic, which were both recorded on a traffic camera the night of the killing.

The video shows the two vehicles passing through a green light at the intersection of 132 Street and 68 Avenue at around 3:30 a.m.

Krupa's body was found shortly after 5 a.m. in the 6900 block of 127A Street.

Anyone with information that could help push the case forward, even seemingly insignificant details, is asked to call IHIT at 1-877-551-IHIT. Those who wish to remain anonymous can instead call Crime Stoppers at 1-800-222-8477.

With files from CTV Vancouver's David Molko